Porous particle fabrication process

ABSTRACT

The method of fabricating spheroid-shaped particles of porous carbon with metal or metallic compound powder dispersed therein, which particles have controlled size, shape and porosity, by dispersing powdered metal or metallic compound material that may comprise fissionable material in precured resin particles, heating the particles in a suspended condition in a fluid medium to spherically shape and cure the particles and then pyrolyzing the cured particles to produce the spheroid-shaped porous char matrix binding the metal or metallic compound powder together.

United States Patent Inventor Constant V. David 2625 Loring St., SanDiego, Calif. 92109 Appl. No. 719,069 Filed Apr. 5, 1968 Patented Nov.9, 1971 POROUS PARTICLE FABRICATION PROCESS 13 Claims, 4 Drawing Figs.

U.S. Cl 264/0.5, 264/44 Int.Cl G2lc2l/00 Field of Search 264/l 5, 43,44.0.5; 176 91 SP References Cited UNITED STATES PATENTS 4/ l 963Bickerdike et al 3,179,722 4/1965 Shoemaker 264/15 x 3,179,723 4/1965Goeddel 264/15 x 3,270,098 8/1966 Barr et al. 264/05 PrimaryExaminer-Benjamin R. Padgett Assistant ExaminerS. R. HellmanAttorney-Carl R. Brown ABSTRACT: The method of fabricatingspheroid-shaped particles of porous carbon with metal or metalliccompound powder dispersed therein, which particles have controlled size,shape and porosity, by dispersing powdered metal or metallic compoundmaterial that may comprise fissionable material in precured resinparticles, heating the particles in a suspended condition in a fluidmedium to spherically shape and cure the particles and then pyrolyzingthe cured particles to produce the spheroid-shaped porous char matrixbinding the metal or metallic compound powder together.

PAIENTEDNUV s IBII 3.619.428

' SHEET 1 BF 2 ADDITIVES HEAT I HEATING 8I fez g PRESSURE PRECURING ISMALL COOLING Z LARGE '6 PARTICLES ii PARTICLES CRUSH'NG coARsE p22scREENs l9 7 FINE SCREENS F |G 4 SPHEROIDIZATI I SPHEROIDIZATIO (52 HOTUSING HOT USING HEATING a GAS GASEOUS LIQUID LIQUID CURING BED BED I 254 GAS CURING FLUID CURING COOLING SETTLING a SETTLING a EXTRACTIONExTRAcTIoN CRUSH'NG 30 I 66 coARsE 58 I COOLING I COOLING SCREENS MESNGr I I WASHING a FINE DRYING SCREENS 62 -34 SORTING a CLASSIFYINGINVENTOR. FINAL CONSTANT V. DAVID POROUS BY F PART'CI-E W? M PRODUCTATTORNEY PATENTEUuuv 9 l97l 3,619,428

SHEET 2 BF 2 use I64 I f-"n78 FIG.3

PRESSURIZED GAS ' Log I I4 HEATED GAS F IG. 2

IN VENT OR. CONSTANT V. DAVID BY zm/zgdw ATTORNEY BACKGROUND OF THElNVENTION phite matrix is porous and these gaseous fission productscould escape and mix with the reactor cooling fluid, which isundesirable, unless a gastight barrier is provided between thefissionable materials and the cooling fluid. Furthermore, voids mustalso be provided around the fissionable material within this gastightbarrier; otherwise the release of the gaseous fission products and: theswelling of the fuel material would create very high pressures thatcould not be contained by the structure of the fuel elements.

There is a known particle structure concept for coating a particletoffissionable material with a gas storing buffer and a.

gastight shell. This concept is generallyknown asthe coated particleconcept for fuel elements of gas cooled nuclear reactors. In thisconcept the fissionable-material, such as a carbide of the heavyfissionable elements enumerated above, comprises a solid sphericalparticle having a diameter ranging from 20 microns to 500 microns, asdeemed most desirableforthe coating operation. The center particle iscoated with a distended (density less the theoretical, porous)graphite/(or carbon),layer called the buffer. The buffer layer thicknessmay range from a fraction of thepatticle radius to more than theparticle-radius. This layer may have between 20 to 60 percent voids-andis relatively soft in the sense that it can be crushed if and when thecenter,particleexpands. This-buffer layer is in turn coated with anotherlayer of dense, highly laminated (oriented) pyroly tic carbon layer thatexhibits high strengthin-the circumferentialdirection and gas tightness.in the radial direction to function properly as a gastight pressurevessel.

The shell coating thickness can vary between a fraction of the partialradius to more than this value. As the nuclear reactor keeps operating,the expansion of the particle crushes part of the buffer layer againstthe shell and in principle enough void volume can still be availableforstorage of the gaseous fission products under pressure, contained bythe shell so that the shell does not crack under the circumferentialtension stresses developed andlimits the amount of stresses transmittedto the matrix whichholds the coated particles together.

ln the coated particle concept, the coating of the particles consists oftwo layers. The outer layer (shell) is easily applied, using standardcarbon coating techniques such as levitation in an ascending stream of ahothydrocarbonaceous gas such as methane. The inner'layer (buffer) ismuch more-difficult and costly to apply. Furthermore, the degree ofdistension and the crushing strength desired as being optimum cannotalways be obtained. ln addition, each coating layer thickness variesfrom particle to particle in the same coating batch around the meanvalue specified. Since the two layers are applied sequentially, the twotolerance spreads compound and the tolerances on the overall coatingthickness are consequently very wide, which degrades the particleperformance as based on the ideal mean specified value.

For these reasons, redesign of'the basic coated particle concept hasbeen attempted so that the inner layer coating (buffer) can beeliminated altogether. Since voids must still be provided for theexpansion of the fissionable materials and the storage of the gaseousfission products, the inner particle must bpbrous and in such a way thatwhen the solid material in it expands, this expansion can take place atthe expense of the pores (voids). For instance, unless the particlemelts, a central hole in the particle would not keep the particle outerdiameter from increasing. Accordingly, it is necessary to disperse thesolid particle, broken up into a fine dust or powder into a porousgraphitic matrix to replace the buffer-coated-solid-particle. Such aspherical porous particle then requires only one coating, the shelllayer. As long as the carbon, fissionable material and void contents ofthis new porous particle are similar to that of thebufier-coated-particle previously described, it will perform the same inthe nuclear reactor, and the undesirable layer is eliminated.

In order to operate efficiently, the porous particle must be spherical,to minimize the shell thickness for a specified peak pressure appliedinternally at the end of the fuel element life period. The fabricationof such a porous particle should therefore lead to spherical particles,prior to the shell coating operation. There are two known processes foraccomplishing this. They are the Sol-gel process and the conglomerationof powdered fissionable material and carbon ina charred resin binderprocess.

The Sol-gel process that is well knownin physico-chemistry, leads tocrystallites of carbides of .the fissionable metals or metalliccompounds dispersed. in a graphite porous matrix. The metal content, thegraphite matrix bulk density and the strength, of that matrix materialobtainedby this process are not easy to obtain as required. Furthermore,the fissionable metals or metallic compounds can only be obtained in the.form of a carbide compound. Other refractory compounds of fissionablemetals such as borides or beryllides that offer additional advantagescannot be used. Thus this process lacks the flexibility of parametervariation required to optimize the] porous particle. The other knownfabrication process is based on the use. of a mixture of fissionablematerial. powder, carbon dust and a binder such as furfural phenol, thatupon curing and pyrolyzation producesthe-graphite char matrix desired.The graphite matrix so fabricated is not very strong and the porousparticlesobtained this way muststill be spheroidized.

mechanically.

SUM MARY OF THE INVENTION The porouszparticle fabrication process ofthis invention cles of porous material with a metal or metallic compoundpowder including fissionableelements dispersed therein and whichparticles have a controlled size, shape and porosity. The process isparticularly applicable for dispersing particles of fissionable-materialsuch as Uranium, Thorium and/or Plutonium, or other suitable materialsin a porous graphite particle that upon the completion of the processmay be provided with a gas sealing shell. The end particle product ispreferably spheroid to allow the shell coating to be'applied tothe.particle so that it has auniform thickness. This latter structurehas particular end application as a nuclear reactorfuel.

ln employing the processes, the metallic compounds or metal powderis-mixed with a filler material, as for example carbon in the fonn ofsmall flakes or chopped fibers, and with a resin thatis capable of beingpyrolyzed to provide a suitable. char or graphite binder that has thedesired porous composition. The resin, powder and additives are mixedtogether with the powder having a particular small sizethat issufficientlysmall, relative to the final size porous particles, toprovide suitable dispersion of the powder in the final particle-product.The mixed composition is then heated and precured and is then cooled toasolid form. The solid composition is crushed to a particle-size thatdetermines the size of the end porous particle. The crushed particles orgrits are sorted by known screening techniques to obtain the desiredsized particles, with large size particles being returned to berecrushed in the crushing step and the smaller size particles, ifdesired, being returned to the mixing step to increase the operationyield. The desired size particles have a rather ununiform shape thatgenerally resembles gravel. Where it is desired that the end particlehave this sort of shape, then the particles at this point can bedirectly moved to the step of pyrolyzing where the odd shaped particlesare raised to a sufficient temperature that the resin is chaired.However, for most applications it is desirable,

and it is a feature of this invention to provide an end particle havinga spheroid shape. Thus the sized particles or grit in the precured stateare supplied to a heated environment that may comprise a gas or liquidbed, where the particles are immersed in the fluid that is heated to thetemperature required to melt the resin in the particles and also to curethe resin. The particles are sufficiently dispersed in the fluid so asnot to contact and join other particles and by being suspended in thefluid in a melted state are subjected to surface tension forces thatcauses the particles to assume a spherical shape. Thus in this step, theheated fluid bed functions to spheroidize the particles and also to curethe particles.

Where the particles are inserted into a gaseous fluid bed, then theoutput particles are cooled and directly sorted and classified for thepyrolyzation step. However, where a liquid bed is employed, theextracted particles are passed through a solvent bed that removes theliquid of the liquid bed. The particles are then cooled,sorted,classified and transported in a known manner to an oven having atemperature sufficiently high to char the resin.

Thus it may be seen that the process of this invention allows the exactproportion of each component of the porous end particles to be easilycontrolled and obtained. Further the chemical compound form of thefissionable material or other metals or metallic compounds dispersed inthe porous particle is not limitative so long as it can be reduced to apowder form having a sufficiently small size. The addition of beneficialcomponents to the basic mixture is made easy and controllable where itis desired to add additives that may improve the final charred productor aid in the process. The spheroidization of the particles occursautomatically without enlarging the final product or obtaining varyingshapes, since it is based upon surface tension action. Also the use offluid beds to obtain the spheroidization of the particles allow the useof fluid levitation processes to obtain an even distribution of theparticles and thus avoid agglomeration as well as obtaining suffrcienttime in the heated environment to cure the resin. The process furtherallows easy recycling of particles to obtain optimum and controlled sizeand curing.

Therefore it is an object of the present invention to provide a new andimproved fabrication process for fabricating porous particles.

It is another object of this invention to provide a new and improvedporous particle fabrication process in which the exact proportion ofeach of the components of the porous particles can be easily controlledand obtained.

It is another object of this invention to provide a new and improvedporous particle fabrication process that may be easily automated.

It is another object of this invention to provide a new and improvedporous particle fabrication process that provides spheroid particlesthat may be charred in a nonagglomerating condition.

Other objects and advantages of this invention will become more apparentupon a reading of the following detailed specification and anexamination of the drawings in which:

FIG. 1 is a block diagram of the steps of the fabrication process ofthis invention.

FIG. 2 is a schematic view of a gaseous bed curing process apparatus.

FIG. 3 is a schematic view of a liquid bed curing process apparatus.

FIG. 4 is a cross-sectional view of a porous particle fabricated by thisprocess.

Referring now to FIG. 4, the porous particle that is fabricated by thisprocess comprises a spherical-shaped body 198 of graphite matrixmaterial 200 having voids 204 and fissionable material powder 202dispersed therein. As previously described the spherical-shaped body198, when used in making a nuclear reactor fuel, is coated with agastight shell 106. Thus accumulations of gas within the shell that aregenerated during fission is absorbed by the voids 204 and the porousgraphite matrix material 200. While this process is capable ofdispersing other metal or metallic compounds in a porous particle, ithas particular unique application in the dispersing of fissionablematerials for use in fuel elements for nuclear reactors. It should beunderstood that the cross-sectional illustration in FIG. 4 is enlargedfor purposes of illustration.

The three basic constituents that are mixed in the first step of theprocess comprise the fissionable, metal or metallic compound material inpowder form, the additives of filler material and the uncured liquidresin or uncured resin in solid particle form. The metallic compound maycomprise any suitable metal compound, such as but not limited to,carbides, borides, beryllides, nitrides, oxides, silicides, or any othersuitable metal or metallic compound. This fissionable material may bemixed in any suitable form, such as a chemical compound form includinguranium, plutonium, thorium, or any other suitable fissionable materialor metals. The metallic compound or metal is introduced into the processin powder form comprising small grains having any particular shape witha size range that generally extends between 0.1 micron and 25 microns.The filler material, that may normally comprise carbon or graphite butis not restricted thereto and may comprise other additives to eitherimprove the nuclear fuel material performance or the char properties orboth, is inserted into the mixing step in the form of solid choppedfibers, flakes or as a powder. The filler material is normally used toselectively increase or vary the carbon content of the final particle,to selectively vary the strength of the final product and to provideroutes for gases to escape in the pyrolyzing of the resin. The baseresin can consist of 1 part, 2 parts, or more as required for curing andgood charting characteristics. The uncured resin parts, before mixingcan be in liquid form or in solid fine powder form.

Since a relatively dense char is required as matrix material for theporous particles, only resin systems that can pyrolyze from the curedsolid state are acceptable for this fabrication process. Resin systems,such as thermoplastics, that melt before pyrolyzation is initiated orfoam as gasses are released within the liquid phase cannot be used inthis process. The acceptable or suitable resin systems for use in thisprocess belong either to the addition polymers" type or to thecondensation polymers type. The addition polymer resin type, typified byepoxy resins, are characterized by cross-linking chemical reactions thatdo not release volatiles during the curing process. The condensationpolymer resin type, such as phenolic base resins, polyimide andpolybenzimidazole resins cure in the liquid phase with the release of alarge amount of volatiles until the molecule cross-linking process iscompleted. The pyrolyzation of these cured resins leads to comparativelydenser and stronger char structures. The addition polymer resins cureautomatically with a rate that is temperature de-v pendent once the twoparts have been mixed and the crosslinking reaction has been initiatedwhereas condensation polymer resins cross-link to a degree that is onlya function of the temperature level reached by the resin base.

The mixing step 10, see FIG. 1, can be accomplished by mixing the metalor metallic compound powder with the filler material and then with theresin or by mixing either the metal or metallic compound powder with theresin first and then by adding the filler material, or by mixing theresin with the filler material first and then adding the metal ormetallic compound powder. If the resin is in a solid powder form, themetal or metallic compound powder and the filler material can be addedtogether with the resin powder and mixed. Should the resin be in aliquid form, the metal or metallic compound powder and the fillermaterial are added to either one part of the resin or all parts of theresin before the mixing of the parts. The choice of mixing proceduredepends upon the volumetric ratio of the resin parts and the viscosityof each part or of the mixed parts, with the choice being made to obtainthe most uniform dispersion of the metal or metallic compound and thefiller material with the maximum ease. The mixing step 10 can beperformed by any of the known mechanical apparatus used in the art formixing powder, or powders in liquids, with the understanding that somemeans are preferable to others, depending upon the volumetric ratios ofthe constituents, the size of the powder grains and the viscosity of theresin parts, if liquid.

The preferred volumetric ratio of the total of the various constituentsis between 5 and 50 percent metal or metallic compound powder, between 0and 40 percent filler material and between and 95 percent resin. Atypical mixture has a volumetric ratio of 30 percent metal or metalliccompound, 25 percent filler material and 45 percent resin.

Upon completion of the mixing, step 10, the mixture is heated to atemperature and under pressure, if necessary, for that length of timerequired to precure the resin to a point that it is solid at or belowroom temperature, but liquid at a temperature above the precuringtemperature. The precured solid mixture is then cooled down to atemperature such that the curing process is stopped completely. Theprecured solid mixture is then crushed into a grit form. The grit issieved to sort the grit into mesh sizes. The sieve mesh range can varyaccording to the application but normally extends from a micron size to200 microns. The grit smaller than the 20 micron size is either thrownaway or reprocessed by being reintroduced from the fine screens 19through representative path 22 into the mixing step 10 and mixed withthe tiller material and the metal or metallic compound for mixing withthe resin. The grit larger than the 200 microns size is screened out bycoarse screening 18 and is returned by representative path 20 to berecrushed to bring it to the correct size.

The shape of each individual particle obtained from the sorting steps 18and 19 is in general irregular and similar to gravel. To shape eachindividual grain of the grit to be spherical, the grit is heated to amelted condition and is then processed so that the curing of the resinis completed. Since the resin is melted, provisions must be made to keepindividual particles of the grit from agglomerating during these steps,and the grit must be maintained at the temperature required to completethe resin curing process. Accordingly, at some time, preferably at thebeginning of step 24, the precured resin that is solid at lowtemperature melts when brought to the elevated temperature needed forthe curing. At this point, each individual particle of the grit becomesviscous and deformable under pressure. The surface tension forcesgenerated by the liquid resin within each particle creates anappreciable pressure because of the very small size of these particles.This pressure acts on the particle material in such a way that itssurface is minimized, thereby automatically spheroidizing the particleshape and giving it the spherical shape desired. As the curing proceeds,the particle material becomes more and more viscous until it is a solid.At this point, the material has become tack free and will notagglomerate into a solid mass. The curing process can now be completedwithout the particles agglomerating.

The heating of the particles is accomplished in a manner that they donot touch and remain separated at all times during curing and until theyhave become solid and tack free. This is accomplished by keeping orsuspending the particles for a given period of time in a hot fluid,either a gas or a liquid, maintained at or above the curing temperature.The residence time at this temperature must be as long as needed toreach the tack free point and is accomplished by use of gaseous orliquid beds that are discussed separately hereinafter.

GASEOUS BED If the number of particles in a given volume is small, thatis a large mean separation distance between particles compared to themean particle dimension, the probability of contact and agglomerationoccurring will be low and the yield of the operation will be high.Practically, this can be achieved by dropping the cold, precured gritinto an ascending column of hot gas. The residence time (t) of theparticles in the gas column is given by:

where: H is the height of the gas column V, is the mean upward velocityof the gas in the column V, is the ultimate free fall velocity of theparticles with respect to the gas. When V,,=V,, the particles do notfall but remain still with respect to the column walls. Since the sizeof the particles is small, their free fall maximum velocity is low andthe gas column velocity required is also low. Generally speaking,smaller particles will fall more slowly and larger particles will fallfaster. Referring to FIG. 2, the cold, nonspherical particles or grits102 are introduced at the top of a heated gas column 109 by a knownconveyor belt apparatus 100. The particles 102 are deposited on a shaker104 having a screen 106, both of which are vibrated by a vibrator "8through connection !08. The shaker screen 106 functions to provideunifonn disp'ersion of the particles 106 in the rising gas column 109. Agas column housing 112 forms a flue that is supplied with heated gasfrom a gas heater 132. The heated gas passes through expansion space134, through porous plate 124, through the settled and cured particles128, up the column 1 12 and out the opening at the top in the directionof arrows 110. The cured particles 128 collect on the porous plate 126and are vibrated by vibrator through linkage 122 to flow down onto theconveyor belt 130. A cooling jacket 114 for carrying cooling gas orfluid in space 116 is provided for a purpose that will be explainedhereinafter. The entire structure rests on base members 136. and 138.

The particles 102 are heated very rapidly, because of their small sizeand melt as they start falling in the hot gas and start curing. In theliquid state, the particles spheroidize for the reason given earlierand, as they keep curing, harden to the point that they are tack free.At that time the particles may touch without agglomerating and the restof the curing process can be performed during the remainder of the fall.The cured particles are then cooled in step 30 and sorted by size rangein step 34 to obtain the correct size of particles desired.

In the situation where particles 128 are of the correct size but havenot been completely cured, then these particles are taken out at line 37and reintroduced at the spheroidization step 24 for further processingat curing temperature to complete the resin curing process. Theadditional polymers" type, such as epoxies, would usually be cured inone pass through the gas column 109 while the condensation polymers"type such as polybenzimidazole, polyimide or polyquinoxaline resins,would be more likely to require reprocessing. In all cases, the gas usedshould be such that it does not react with the particle materials,before and during curing. The gas pressure is set to that amountrequired to correctly control the free fall maximum velocity of theparticles and the heat transfer rate between the gas and the particles.The choice between several suitable gases such as helium, nitrogen,carbon dioxide, or other suitable gases makes possible the adjusting ofthis free fall maximum velocity because of the large differences in gasdensity for given temperatures and pressures.

The gas temperature is high enough to melt the precured resin and alsoto cure the resin to the tack free stage as fast as possible. In orderto keep liquid particles from sticking to the walls of the gas column,two features of the apparatus illustrated in FIG. 2 are used, eitherindividually or in combination. The column cross section is smaller atthe top and larger at the bottom giving an outward slope to the wall112. The gas column wall 112 is also cooled so that a cooler gasboundary layer is maintained adjacent the wall. This keeps the liquidparticles from touching the walls and a liquid particle in the cold gasboundary layer solidifies and becomes as tack free as it was in theprecured stage.

LIQUID FLUID BED The essential differences between the liquid bed andthe preceding gas bed are that the rate of settling is much slower in aliquid than it is in a gas, the surface tension forces acting on theparticle liquid interface are smaller than they are in the case of a gasand correspond to the difference between those due to the surfacetension of the resin and those due to the surface tension of the bedliquid, and the liquid if not self removing must be removed from theparticles in a washing and drying step.

In using a liquid bed, see FIG. 3, the loading, curing and unloadingproceeds in the following manner. A suitable liquid 178 is placed in aliquid tight container 162. Heating jacket 164 provides a heating space166 for containing hot gas or fluid from any suitable source (not shown)for heating the liquid 178 to the temperature required for melting andcuring the particles. A connecting container 191 has a reservoir supplyof liquid 192 therein that is used to maintain a given level of liquid178 in the container 162. A suitable gas under pressure is appliedthrough opening 190 to force the liquid 192 through connector 193 andinto the container 162 to maintain the given level.

The particles to be shaped to a spheroid are transported on a conveyor152 of known construction and deposited in a shaker 158 having a screen160. A vibrator 154 is connected by linkage 156 to vibrate the shaker158 and disperse the particle grits 150 evenly in the heated liquid 178.The particles when dusted on the free surface of the hot liquid 178 meltand start falling slowly in a spherical shape in the liquid and curewhile settling. When enough particles have settled at the bottom of theliquid column 178, the drive motor 168 is energized to operate thehelical screw extractor 172 to move the settled curred particles 174 tothe container 191 where the particles pass out through opening 180 to aconveyor belt 182. The conveyor belt 182 may be made of a porousmaterial that allows the liquid to pass therethrough into the sump 184,where the liquid is moved by a suitable line 186 and pump 188 to thechamber 191 to be added to the liquid 192. Suitable valves may beemployed in line 186 to prevent the entry of back pressure gas from thegas pressure applied through opening 190 to the container 191. It shouldbe understood that the extraction of the particles 174 at the bottom ofthe settlement without disturbing the upper part of the settlementallows the continuous automatic fabrication process to be accomplishedby draining the excess liquid from the particles into the sump 184. Alsosuction or mechanical means can be used to more rapidly draw theparticles and fluid from the opening 180. The pressure applied to theliquid 178 is relatively unimportant and could be anything practicalsuch as atmospheric pressure.

Upon recovery of the particles from the fluid bed, the cured spheroidparticles are then cooled and passed through a known washing and dryingbed step 32 that functions to remove the fluid still on the particlesfrom the fluid bed. The solvent used to remove the bed liquid, unlessthis liquid can be disposed of by evaporation process under heat and/orvacuum conditions, depends upon the nature of the fluid used in the bedliquid. The slurry of particles and liquid is mixed with the solvent andagitated to remove all liquid and the particles are then separated fromthe solvent either by known gravitational processes or throughcentrifugation settling. This can be repeated as many times as requiredto clean the particles adequately. Upon the last cleaning operation, thewet particles are dried by evaporation of the solvent and are thensorted out by size range as described relative to the process step 34previously described.

It may thus be understood that the steps 24 through 32 may beaccomplished either by using the gaseous bed or the liquid bed. However,the particles obtained in the sorting and classifying step 34 fromeither process are substantially the same. The dry cured particlesobtained and sorted out in the sorting and classifying step 34 are thenmoved in any known type of container directly into an oven that is at atemperature required to drive all the volatile elements of the resin outand produce the char products desired, which holds the metallic compoundpowder together in a porous binder. The pressure applied to theparticles during this pyrolyzation process is unimportant but thevolatiles m5: be allowed to escape. This step completes the fabricationprocess of the uncoated porous particles. Upon final sorting out, if sodesired, these particles are ready for the coating operation if acoating is desired.

As previously described, the particles or grits leaving the crushingstep have a nonuniform shape that generally resembles gravel. Thereare'certain uses for charred end particles having these shapes. Thus isa modification of this invention, the mixed composition mixed in step 10is heated 52 to the curing temperature of the resin and is cured andcooled 54 to a solid form. The solid composition is crushed 56 to a gritform that generally resembles gravel and has a particle size thatdetermines the size of the end porous graphite particle. The crushedparticles or grits are sorted by screening techniques, with large sizeparticles removed by course screening 58 and returned 66 to be recrushedin the crushing step 56. Smaller size particles are removed by finescreening 60 and if desired, are returned 62 to the mixing step 10 toincrease operational yield. The sized particles or grits are then 64pyrolyzed 38 in the manner previously described.

While 1 have shown and described a specific form of my invention, it isto be understood that various changes and modifications may be madewithout departing from the spirit of the invention as set forth in theappended claims.

Having described my invention, 1 now claim:

1. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein comprising the steps of,

mixing a powdered material of metal or metallic compounds with a resin,

precuring the resin with the mixed material dispersed therein to a solidform,

crushing the solid mixed material to particle grits having a given rangeof sizes,

dispersing the grits in a fluid heated to the melting temperature of theresin forming spheroid particles,

curing the resin in the spheroid particles,

and charring the resin in the cured spheroid particles to a porousgraphite binder.

2. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein as claimed in claim 1 including the steps of,

settling the cured spheroid particles in the heated fluid,

and extracting the cured spheroid particles from the fluid.

3. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein and having a given size as claimed in claim 2 including the stepof,

sorting the cured spheroid particles as to size.

4. The process for the fabrication of spheroid porous gra' phiteparticles having powdered material of metal or metallic compoundsdispersed therein as claimed in claim 1 in which,

the dispersing step including shaping the grits to a spheroid by surfacetension forces,

and dispersing the spheroid particles sufiiciently in the fluid as tosubstantially prevent agglomeration of the particles until the resin inthe particles is cured.

5. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein as claimed in claim 4 in which,

the dispersing and curing steps including dispersing the grits in aheated liquid bed,

moving the spheroid particles through the liquid bed by gravity,

curing the resin in the spheroid particles during the movement throughthe liquid bed,

and removing the liquid from the cured spheroid particles.

6. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein as claimed in claim 4 in which,

the dispersing and curing steps including dispersing the grits in aheated gaseous bed,

moving the spheroid particles through the gaseous bed by gravity,

and moving the gas in the gaseous bed upwardly with sufficient force toreduce the speed of movement of the spheroid particles whereby the resinin the particles is cured during the movement.

7. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein as claimed in claim 1 including the steps of,

cooling the precured mixed material and resin,

coarse screening the particle grits and returning large size grits tothe crushing step,

and fine screening the particle grits and returning small size particlesto the mixing step.

8. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein and having a given size as claimed in claim 1 including the stepof,

mixing carbon in the form of small particles with the powdered materialand the resin.

9. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein and having a given size as claimed in claim 8 in which,

the mixed powdered material, resin and carbon having a volumetric ratioof 5 to 50 percent powdered material, to 40 percent carbon and 10 to 95percent resin.

10. The process for the fabrication of spheroid porous graphiteparticles having powdered material of metal or metallic compoundsdispersed therein and having a given size as claimed in claim 1 inwhich,

the resin comprising a resin that pyrolyzes from the cured solid state.

1 1. The process of fabrication of given size porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein comprising the steps of,

mixing a powdered material of metal or metallic compound with a resin,

curing the resin with the mixed material dispersed therein to a solidform,

crushing the solid mixed material to particle grits having a given rangeof sizes,

and charring the resin in the cured grit to a porous graphite binder.

12. The process for the fabrication of given sized porous graphiteparticles having powdered material of metal or metallic compoundstherein as claimed in claim 11 in which,

the resin comprising a resin that pyrolyzes from the cured solid state,

and mixing carbon in the form of small particles with the powderedmaterial and the resin.

13. The process for the fabrication of given sized porous graphiteparticles having powdered material of metal or metallic compoundstherein as claimed in claim 11 including the steps of,

cooling the cured mixed material and resin,

coarse screening the particle grits and returning large size grits tothe crushing step,

and fine screening the particle grits and returning small size grits tothe mixing step.

* i It i

2. The process for the fabrication of spheroid porous graphite particleshaving powdered material of metal or metallic compounds dispersedtherein as claimed in claim 1 including the steps of, settling the curedspheroid particles in the heated fluid, and extracting the curedspheroid particles from the fluid.
 3. The process for the fabrication ofspheroid porous graphite particles having powdered material of metal ormetallic compounds dispersed therein and having a given size as claimedin claim 2 including the step of, sorting the cured spheroid particlesas to size.
 4. The process for the fabrication of spheroid porousgraphite particles having powdered material of metal or metalliccompounds dispersed therein as claimed in claim 1 in which, thedispersing step including shaping the grits to a spheroid by surfacetension forces, and dispersing the spheroid particles sufficiently inthe fluid as to substantially prevent agglomeration of the particlesuntil the resin in the particles is cured.
 5. The process for thefabrication of spheroid porous graphite particles having powderedmaterial of metal or metallic compounds dispersed therein as claimed inclaim 4 in which, the dispersing and curing steps including dispersingthe grits in a heated liquid bed, moving the spheroid particles throughthe liquid bed by gravity, curing the resin in the spheroid particlesduring the movement through the liquid bed, and removing the liquid fromthe cured spheroid particles.
 6. The process for the fabrication ofspheroid porous graphite particles having powdered material of metal ormetallic compounds dispersed therein as claimed in claim 4 in which, thedispersing and curing steps including dispersing the grits in a heatedgaseous bed, moving the spheroid particles through the gaseous bed bygravity, and moving the gas in the gaseous bed upwardly with sufficientforce to reduce the speed of movement of the spheroid particles wherebythe resin in the particles is cured during the movement.
 7. The processfor the fabrication of spheroid porous graphite particles havingpowdered material of metal or metallic compounds dispersed therein asclaimed in claim 1 including the steps of, cooling the precured mixedmaterial and resin, coarse screening the particle grits and returninglarge size grits to the crushing step, and fine screening the particlegrits and returning small size particles to the mixing step.
 8. Theprocess for the fabrication of spheroid porous graphite particles havingpowdered material of metal or metallic compounds dispersed therein andhaving a given size as claimed in claim 1 including the step of, mixingcarbon in the form of small particles with the powdered material and theresin.
 9. The process for the fabrication of spheroid porous graphiteparticles having powdered material of metal or metallic compoundsdispersed therein and having a given size as claimed in claim 8 inwhich, the mixed powdered material, resin and carbon having a volumetricRatio of 5 to 50 percent powdered material, 0 to 40 percent carbon and10 to 95 percent resin.
 10. The process for the fabrication of spheroidporous graphite particles having powdered material of metal or metalliccompounds dispersed therein and having a given size as claimed in claim1 in which, the resin comprising a resin that pyrolyzes from the curedsolid state.
 11. The process of fabrication of given size porousgraphite particles having powdered material of metal or metalliccompounds dispersed therein comprising the steps of, mixing a powderedmaterial of metal or metallic compound with a resin, curing the resinwith the mixed material dispersed therein to a solid form, crushing thesolid mixed material to particle grits having a given range of sizes,and charring the resin in the cured grit to a porous graphite binder.12. The process for the fabrication of given sized porous graphiteparticles having powdered material of metal or metallic compoundstherein as claimed in claim 11 in which, the resin comprising a resinthat pyrolyzes from the cured solid state, and mixing carbon in the formof small particles with the powdered material and the resin.
 13. Theprocess for the fabrication of given sized porous graphite particleshaving powdered material of metal or metallic compounds therein asclaimed in claim 11 including the steps of, cooling the cured mixedmaterial and resin, coarse screening the particle grits and returninglarge size grits to the crushing step, and fine screening the particlegrits and returning small size grits to the mixing step.